Elizabeth Huyhn1, Elodie E. Huguet2, and Clifford R. Berry3 1 VCA West Coast Specialty and Emergency Animal Hospital, Fountain Valley, CA, USA 2 Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL, USA 3 Department of Molecular Biomedical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, NC, USA Nuclear scintigraphy uses radioactive labels called radionuclides that are linked to an active marker for a specific physiologic process in the body, called a radiopharmaceutical, which is injected into the patient. The physiologic marker delivers the radioactive label to an area of interest to the clinician. Employing a special detector called a gamma camera, the gamma rays emitted from the radionuclide are counted, and can be related to organ function. A radiopharmaceutical injected into the patient consists of two components: (i) a radionuclide that emits gamma radiation and (ii) a pharmaceutical that will target the radionuclide to the physiology of interest. A variety of radionuclides are available but, commercially, technetium (99mTc) is favored because (i) it has a halfâlife of approximately 6 hours which will allow sufficient time for images to be obtained but avoid excessive radiation exposure to the patient and handlers; (ii) it emits gamma radiation at energies such that the electromagnetic emissions are sufficiently able to escape from the body and is in the detectable range for gamma cameras; (iii) it has a simple chemistry so that it can be bound to a variety of pharmaceuticals to target different physiologies within the body, and (iv) when injected as sodium pertechnetate, it acts like iodide and is taken up by the salivary and thyroid glands. Although nuclear scintigraphy is not used commonly due to the accessibility of other advanced imaging techniques, there are specific applications that are still indicated for imaging using scintigraphy. These applications of nuclear scintigraphy in veterinary medicine can include glomerular filtration rate studies, shunt detection, liver function, bone metabolism, thyroid function, and mucociliary function. The benefit of glomerular filtration rates (GFR) studies is to detect renal dysfunction before renal azotemia is apparent, as diseased kidneys do not regulate GFR well. Types of GFR studies include (i) the imaging studies where the regions of interests (ROI) are placed over the kidneys and (ii) plasma clearance studies where the ROI is placed over the heart. The imaging studies can determine the individual kidney GFR data whereas the plasma clearance studies provide global GFR data. After the ROIs are placed over the respective anatomy, counts are made over time and a chart is produced (Figure 5.1). FIGURE 5.1 Quantitative renal scintigraphy chart denoting the right (blue line) and left (red line) kidneys in relation to the renal counts over time in a normal patient. Renal counts are calculated by drawing regions of interest over the kidneys and noting the accumulation of radiopharmaceutical over time. In a normal patient, the arterial blush is seen early in the curve. The peak renal activity for both right and left kidneys is at the highest point, which is 3 minutes. Source: Courtesy of Daniel GB, Berry CR, Textbook of Veterinary Nuclear Medicine. Portal scintigraphy can be used for congenital or acquired portosystemic shunt (PSS) detection and is considered a noninvasive procedure. In patients with PSS, the radiopharmaceutical bypasses the liver and goes to the heart first and later accumulates in the liver. Two techniques can be used for PSS detection: the radiopharmaceutical can be administered transrectal or transsplenic. For the transsplenic technique, radiopharmaceutical is injected into the splenic parenchyma parallel to the long axis of the spleen (Figure 5.2). PSS patterns observed in this study include portoazygous, single portocaval, splenocaval, and internal thoracic shunts. Single shunts can be distinguished from double or multiple shunts. The termination of the shunt and number of vessels can also be determined. FIGURE 5.2 Transsplenic portal scintigraphy in a normal dog. The cranial aspect of the patient is to the right of the image and the dorsal aspect is at the top of the image. Note the increased radiopharmaceutical uptake in the spleen. The curvilinear track caudal to the spleen is the small amount of radiopharmaceutical left in the syringe after injection. The dots ventral to the liver are markers to delineate the region of the liver. Source: Courtesy of Daniel GB, Berry CR, Textbook of Veterinary Nuclear Medicine. To determine liver function, a hepatic perfusion index
CHAPTER 5
Nuclear Scintigraphy
Overview
Basic Physics
Uses and Advantages
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